The Effect of Nitrogen Supplementation by Applying Livestock Waste Compost on the Freezing Tolerance of Japanese Chestnut

摘要

In the context of global warming, freezing injury has tended to occur more frequently in cultivated Japanese chestnuts. To elucidate the cause of such freezing injury, we studied the effect of nitrogen (N) supplementation from livestock waste compost added to gray lowland soil on the freezing tolerance of Japanese chestnut trees in terms of their carbohydrate, water and N statuses. We also investigated the relationship between the endodormancy status and freezing tolerance of trees grown with or without livestock waste compost application. The freezing tolerance of Japanese chestnut trees planted in an excess of livestock waste compost was apparently lower than for trees grown only in gray lowland soil. The current season's shoots from trees grown in soil only had the highest total sugar content, but the differences in total sugar content were not statistically significant, even though the N supplementation from livestock waste compost reduced the freezing tolerance. By contrast, higher water and N contents were recorded in the current season's shoots grown in the presence of excessive livestock waste compost than in those grown in gray lowland soil only, all of which led to a reduction in the rate of winter survival among trees treated with livestock waste compost. The date of reaching 70% bud sprouting was delayed by one month or more, but bud break initiation was accelerated by the application of livestock waste compost, possibly due to a disturbance in the normal endodormancy progression. Collectively, these results suggest that normal endodormancy progression can be obstructed by higher water and N contents in trees treated with excessive livestock waste compost; thus, freezing tolerance sufficient to survive winter could not be acquired.